Occupational studies are conducted to identify and quantify chemical and other causes of cancer and to understand mechanisms of carcinogenesis. Etiologic investigations utilize sophisticated industrial hygiene methods to assess occupational exposures and biochemical components to characterize exposure-response patterns, to elucidate mechanisms of carcinogenic action, and to evaluate individual susceptibility factors. Methodologic studies are designed to improve study techniques and to provide direction for future research. Major etiologic investigations focus on working populations exposed to benzene, trichloroethylene, other organic solvents, formaldehyde, diesel exhausts, combustion products, electromagnetic fields, pesticides, and silica. Findings linking cancer with occupational exposures included an excess of nasopharyngeal cancer among workers exposed to formaldehyde; breast cancer among women in Shanghai was associated with employment in the textile industry, medical profession, and the telecommunications industry; breast cancer among Polish women was elevated among those in the electronics industry and among those holding white collar jobs; no cancer association was noted among workers exposed to trichloroethylene at Hill Air Force Base, but lymphoma and breast cancer was associated with potential exposure to a few solvents; laryngeal cancer was associated with asbestos and pharyngeal cancer with cement dust in Swedish construction workers; no cancer excesses were observed among pesticide applicators exposed to DDT in an anti-malarial campaign in Sardinia; chronic obstructive pulmonary disease and restictive lung disease was associated with lung cancer in Swedish construction workers; lung cancer among workers in mines and pottery factors was evaluated in relation to silicosis, silica exposure and other occupational exposures; lung cancer was elevated among Russian workers exposed to linen dust, acids, solvents, and metals; and end stage renal disease was associated with some solvents in a study at Hill Air Force Base and asthma among women in Shanghai was associated with employment as electricians and laboratory technicians and in the production of metal and textile products. Methodologic studies dealt with confounding and exposure misclassification, quantitative exposure assessment, and exposures and urinary mutagenicity in rubber workers. Ongoing projects to evaluate occupational exposures include case-control studies of bladder cancer in Spain and New England, lung cancer in Russia, renal cancer in Eastern Europe, renal cell cancer in the United States, non-Hodgkin's lymphoma in the United States, lung cancer in China, and breast cancer, endometrial, and ovarian cancer in Poland. Ongoing cohort studies of occupational groups include miners with exposure to diesel exhausts; farmers with exposure to pesticides and other agricultural chemicals; women in many occupations in Shanghai; Coast Guard marine inspectors exposed to solvents; shipyard workers exposed to asbestos, paints and welding fumes; and cohorts of industrial workers with exposure to benzene, acrylonitrile, formaldehyde, and solvents.